Question

An organic compound contains C, H and O. 0.25 g of organic compound on combustion produces CO$_2$(g) and H$_2$O(l). When residual gases pass through KOH solution, its mass increases by 0.18 g and when passed through anhydrous CaCl$_2$, the increase in mass of CaCl$_2$ is 0.15 g. Find the mass % of oxygen in the organic compound.

Hint:

In combustion analysis, oxygen content is always calculated by mass difference.

Answer 1

Correct Answer: 73

Step 1: Determine mass of carbon from CO$_2$.
Increase in mass of KOH = mass of CO$_2$ absorbed = 0.18 g
\[ \text{Moles of CO}_2 = \frac{0.18}{44} = 0.00409 \]
\[ \text{Mass of carbon} = 0.00409 \times 12 = 0.0491\ \text{g} \]
Step 2: Determine mass of hydrogen from H$_2$O.
Increase in mass of CaCl$_2$ = mass of H$_2$O absorbed = 0.15 g
\[ \text{Moles of H}_2\text{O} = \frac{0.15}{18} = 0.00833 \]
\[ \text{Mass of hydrogen} = 0.00833 \times 2 = 0.01667\ \text{g} \]
Step 3: Determine mass of oxygen by difference.
\[ \text{Mass of oxygen} = 0.25 - (0.0491 + 0.01667) = 0.18423\ \text{g} \]
Step 4: Calculate mass percentage of oxygen.
\[ %\ \text{Oxygen} = \frac{0.18423}{0.25} \times 100 = 73.69 \approx 73 \]